1. Field of the Invention
The invention relates to a method for producing multi-layer printed board, more specifically, a method for producing multi-layer printed board having holes on the top board thereof.
2. Description of the Prior Art
In the past, film-shaped adhesives were frequently used for producing a multi-layer printed board. When the adhesive is used for laminating the multi-layer printed hole board in the first layer, it is necessary to laminate the printed board so that the adhesive does not extrude into the holes of the layer, since modules are soldered onto the copper pattern in the holes. Therefore, holes of the film-shaped adhesive are perforated larger than those of the printed board so that the adhesive does not extrude into the holes of the printed board even if the adhesive melts when it is cured.
Another method is that the adhesive extruded into the holes is removed, for example, by a hot knife, after the melted adhesive is filled in the holes of the printed board without taking any means at adhesion.
Another method for manufacturing a multi-layer board is disclosed in the Japanese laid-open publication No. 3-194998, in which a dry film resist is provided on the outer surface of the metallic foil for filling the aperture end of the through-holes, then the heat and pressure are applied to the printed board so that the resin which forms the prepreg does not adhere to the metallic foil.
FIG. 10A shows a sectional view of a conventional method for manufacturing a multi-layer printed board. In FIG. 10A, 1 is a lower layer board in the multi-layer printed board. 1a is a copper pattern formed on the board 1. 2 is an upper layer board having holes which is referred to below as a hole board. 2a is a copper pattern formed on the hole board 2. 2b is a hole portion in the hole board 2. 3 is a film-shaped adhesive. In FIG. 10A, the radius of the film-shaped adhesive is larger than that of the copper pattern formed on the board 1.
In the method for perforating large holes in the film-shaped adhesive rather than the printing hole board, if the holes of the film-shaped adhesive are larger than those of the printed board, an adhesion failure sometimes happens by the influence of decrease of the adhesion area as shown in FIG. 10A. And also, if a larger adhesion pressure is applied to the printed board for forcing the adhesive strength, the hole portion 2b of the upper layer board 2 happens to distort.
In the method for removing the extruded adhesive by using a hot knife as shown in FIG. 10B, the wiring patterns are sometimes damaged by the knife blade. Since it takes a lot of time to soften the adhesive using the hot knife, it takes a lot of time to remove the extruded adhesive in the holes 2b.
It is a primary object of the present invention to provide a method for producing a multi-layer printed board, in which the removing process of the adhesion extruded in the holes can be omitted, and also, the deformation of the holes can be avoided. Further, the amount of the adhesive can be economically used.
It is another object of the present invention to provide a method for producing a multi-layer printed board, in which thermoplastic resin sheet can be easily removed from the hole board after the printed board has been formed.
It is another object of the present invention to provide a method for producing a multi-layer printed board, in which the deformation of the multi-layer printed board can be easily controlled.
It is another object of the present invention to provide a method for producing a multi-layer printed board, in which high reliability of adhesion can be obtained.